fortress
nounUK /ˈfɔː.trəs/
US /ˈfɔːr.trəs/
A very strong building that keeps people safe from attacks.
The old fortress stood on top of the hill and had thick stone walls.
OTHER MEANINGS
2. A place that is very well protected and hard to enter.
The company built a digital fortress to keep its data safe.
3. Something that is very strong and cannot be easily broken or changed.
Her calm mind was a fortress against worry.
4. A heavily guarded military base or strong point.
Soldiers guarded the mountain fortress day and night.